The overall objective of this investigation is to assess the effects of interventions on infarct size following an acute experimental coronary artery occlusion, using a technique which can measure directly the volume of the infarcted myocaridum. Thus in order to determine and quantify directly both the short- and long-term effects of several interventions on myocardial salvage without relying on indirect methods, the left coronary artery was occluded in 880 rats; they were then given either no treatment or one of the following interventions: 1. hyaluronidase, an enzyme which hydrolyzes interstitial glycoproteins, 1500 NF units/kg i.v. 5 minutes and 24 hours after occlusion; 2. cobra venom factor, a protein which depletes the third component of complement, 20 units kg i.v. 5 minutes after occlusion; 3. a glucocorticoid: A. hydrocortisone, 50 mg/kg i.v. 5 minutes after occlusion; B. the five-fold more potent methylprednisolone: (i) 50 mg/kg i.v. 5 minutes after occlusion, or (ii) 50 mg/kg i.v. 5 minutes after occlusion followed by 50 mg/kg i.m. 3, 6, and 24 hours after occlusion; or 4. reserpine, an agent which depletes the heart of catecholamines, 0.5 mg/kg i.m. once on each of the 3 days prior to occlusion. The animals were sacrificed either 2 days after occlusion, i.e., after the infarct was completely healed. The amount of preserved myocardium was then assessed by 2 independent techniques; planimetric measurement of serial hostologic sections and creatine kinase activity of the whole left ventricle. The amount of normal myocardium preserved at 21 days post-occlusion was significantly increased, by 22.3 plus or minus 7.8% (p is less than 0.25) following the administration of hyaluronidase, by 25.3 plus or minus 5.8% (p is less than 0.005) following cobra venom factor, by 14.5 plus or minus 6.9% (p is less than 0.05) after hydrocortisone, by 20.8 plus or minus 8.2% (p is less than 0.025) after the single dose of methylprednisolone, by 20.0 plus or minus 3.9% (p is less than 001) after the 4 doses of methylprednisolone, and by 10.2 plus or minus 3.7% (p is less than o.o5) as a result of pretreatment with reserpine.